1. Field of the Invention
The present invention relates to a slider used for supporting a movable article, and more particularly to such a slider utilizing surface elastic waves.
2. Description of the Prior Art
A low friction is required for the slider for achieving its objective. For this purpose, the conventional sliders can be classified into the following types with respect to the supporting method of the movable article on a guide:
(A) the contact type, utilizing sliding bearings or rolling bearings such as ball bearings:
(B) a non-contact type utilizing compressed air: and
(C) a non-contact type utilizing a magnetic repulsive or attractive force.
The sliders of the (A) type are applied in various fields because of the advantages of low cost, compactness, light weight and low noise. On the other hand, they are associated with the drawbacks of requiring lubrication, and dust-preventive structure leading to cumbersome maintenance.
Also for the purpose of maintaining the movable article at a fixed position, the slider of (A) type has to be subjected to a certain servo operation for positioning, or has to have a certain holding mechanism.
On the other hand, the sliders of the (B) or (C) type have far better durability said serviceability because of the non-contact structure. Also in the case of holding the movable article at a fixed position, the positioning can be achieved by simply terminating the generation of compressed air or magnetic field, since, in the absence of the compressed air or magnetic field, the movable article comes into contact with the guide member and is supported at a determined position by the frictional force thereof. However, the slider of (B) type requires a device for supplying compressed air and is therefore associated with the drawbacks of bulkiness and a high electric power consumption. Besides, the slider of (B) type suffers from a complicated structure because of the presence of pumps and valves for controlling the compressed air pressure.
Also the slider of (C) type requires means for generating the magnetic field, and therefore suffers from bulkiness and a high electric power consumption. Besides, it is associated with the problem of the effect of leaking magnetic field on other devices. The use of a permanent magnet instead of an electromagnet can resolve the problem of power consumption, but gives rise to a new drawback of inability to respond to a change in load.
In this manner, the conventional sliders represented by the types (A), (B) and (C) have respective advantages and disadvantages and are unable to properly respond to the recent trend for higher precision and more compact structure.